1. Field of the Invention
The present invention relates generally to a base station system carrying out a radio communication with automobile telephones, portable telephones, etc., in a mobile communication system, and more particularly to the form of a base station constituting the base station system and covering a cell having a small radius, a so-called microcell, and suitable for the microcell.
2. Description of the Related Arts
In a mobile communication system utilizing mobile vehicle-carrying communication apparatuses or mobile portable communication apparatuses (hereinafter referred to generally as mobile stations) typically called automobile telephones or portable telephones, a plurality of radio base stations are placed in a service area allowing communications to provide communication service. Each radio base station (hereinafter referred to simply as a base station) carries out radio communication with mobile stations lying within a cell which that base station covers. Various inventions have been hitherto filed which pertain to the system structure and communication apparatuses such as base station or mobile station. The following are examples of such applications.
1. U.S. Pat. No. 4,777,633 entitled BASE STATION FOR WIRELESS DIGITAL TELEPHONE SYSTEM filed on Aug. 14, 1987.
2. U.S. Pat. No. 5,276,905 entitled MOBILE RADIO TRANSMISSION SYSTEM USING PREFERRED HOME SERVICE AREA filed on Feb. 7, 1990.
3. U.S. Pat. No. 5,321,737 entitled CORDLESS TELEPHONE COMMUNICATION SYSTEM HAVING BASE STATIONS WITH MEMORY FOR QUICK ACCESS TO INFORMATION filed on May 12, 1993.
Referring now to FIG. 9 of the drawings there is illustrated a schematic configuration of a base station system disclosed in the U.S. Pat. No. 4,777,633. The conventional base station system comprises a plurality of base stations 1 each carrying out radio communication with mobile stations 8, and a base station controller 10 connected to a service supplier 2 and serving to control the plurality of base stations 1.
The base station 1 includes a plurality of transceivers provided for each channel, and consisting of a combination of a channel control section 3 and an amplifier 4, a plurality of multiplexers (MUX) 5 distributing information from the base station controller 10 to the transmitter receivers, a timing control section 6 executing timing control of the multiplexers 5, and a radio processing section 7 carrying out radio communications between the transmitter receivers and the mobile stations 8.
The base station controller 10 includes a communication processing section 11 carrying out line communication with the service supplier 2 and carrying out communication with the base stations, a base station control section 12 serving to control base station to base station communication, an interface 13 disposed between the communication processing section 11 and the base station control section 12, and a plurality of echo cancelers 14 corresponding to the MUXs 5 of the base station 1.
The base station 1 in the conventional base station system having the above configuration distributes multiplexed data sent out from the base station controller 10 to the transmitter receivers by use of the MUXs 5. Each transmitter receiver places data into a time slot and carries out radio communication with a predetermined mobile station 8 using a TDMA method. The transmitter receivers are each able to perform simultaneous communication with a plurality of mobile stations 8. On the contrary, information from the mobile stations 8 received by the base station 1 is sent intact to the base station controller 10 for predetermined processing. The base station controller 10 in the conventional base station system performs not only line communication processing associated with the service supplier 2 but also collective management of communication control associated with the base station 1. This means that the base station controller 10 takes charge of control of radio processing between the mobile stations 8 and the base stations 1.
In this manner the conventional base station system causes the base station controller 10 to execute both line communication processing and processing involved in radio communications with the mobile stations 8. This will result in a configuration of a so-called base station controller leading type in which the base station controller predominates over the base stations. For this reason, the scale of the base station controller 10 configuration is enlarged, resulting in a form of system suited to a wider range of cell, a so-called macrocell, for an automobile telephone system and the like. Due to its large-scale configuration, the base station controller 10 is ordinarily constituted of custom-made items.
In order to ensure application over a wider range such as the automobile telephone system, the conventional mobile communication systems elongated the radius of a cell that one base station covers. In recent years, however, it has become desired to reduce the cell radius into a smaller cell, that is, a microcell, and to save the power consumed by transmission and reception, so as to ensure service by the mobile communication system within a restricted range such as underbuilding shopping centers and not to interfere with the action of the other radio apparatuses. A smaller cell will contribute to power saving of each base station, and hence to downsizing of the apparatus.
However, the conventional base station system has a configuration suitable for the macrocell, so that even if it is successfully applied to the microcell by reducing the specifications of the large-scale system, the line service charge will increase since the base station system collectively controls the base stations resulting in frequent communications between the base stations and the base station controller. Because of the fact that the number of base stations increases accordingly as the cell radius is reduced, this will impractically lead to an even greater line service charge.